1. Field of the Invention
The present invention relates to a semiconductor device. More particularly, the present invention relates to a semiconductor device comprising a contact structure in which two types of conductive layers located adjacent to each other are connected to each other by a third conductive layer pattern extending over these two conductive layers.
2. Description of the Prior Art
In integrated circuits, especially in a metal-insulator semiconductor type of integrated circuit, interconnecting lines consisting of polycrystalline silicon layers are generally used. Due to an increase in the degree of integration of integrated circuits, it has been possible to provide a two-layered polcrystalline layer in a multi-level interconnection structure in order to realize a further increased level of interconnection or in order to utilize the two-layered polycrystalline layer as a resistor. A conventional monolayered polcrystalline structure is of a so-called silicon gate structure in which a so-called buried contact structure is adopted to realize a direct contact between the polycrystalline silicon layer and the source or drain diffused layer as disclosed in Japanese Examined Patent Publication No. 50-40835. This buried structure is advantageous for decreasing the size of the contact portion. However, this structure involves a problem in that the formation of a contact window is necessary before the formation of a polycrystalline silicon layer, i.e., before the formation of a source or drain region. Therefore, for the two-layered polycrystalline silicon structure, there is proposed, in place of the buried contact structure, a contact structure in which the diffused layer and the first polycrystalline silicon layer, which are arranged adjacent to each other, are connected to each other by the second polycrystalline silicon layer pattern extending over these two layers. In any event, the formation of a contact window for the previously formed diffused layer or first polycrystalline silicon layer is necessary before the formation of the second polycrystalline silicon layer. Therefore, even if the above-proposed structure is adopted, the diffused layer and the first polycrystalline silicon layer can be connected to each other without the carrying out of any special additional process. Such a contact structure is known from, e.g., the IEEE Journal Of S.S.C., Vol. SC-16, October 1981, pages 444 to 448.